Textbook Question
What energy requirements must be met in order for a reaction to be favorable?
Ch.21 The Generation of Biochemical Energy
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187
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Table of contents
- Ch.1 Matter and Measurements27
- Ch.2 Atoms and the Periodic Table20
- Ch.3 Ionic Compounds8
- Ch.4 Molecular Compounds23
- Ch.5 Classification & Balancing of Chemical Reactions12
- Ch.6 Chemical Reactions: Mole and Mass Relationships28
- Ch.7 Chemical Reactions: Energy, Rate and Equilibrium64
- Ch.8 Gases, Liquids and Solids24
- Ch.9 Solutions52
- Ch.10 Acids and Bases25
- Ch.11 Nuclear Chemistry22
- Ch.12 Introduction to Organic Chemistry: Alkanes57
- Ch.13 Alkenes, Alkynes, and Aromatic Compounds47
- Ch.14 Some Compounds with Oxygen, Sulfur, or a Halogen50
- Ch.15 Aldehydes and Ketones45
- Ch.16 Amines42
- Ch.17 Carboxylic Acids and Their Derivatives57
- Ch.18 Amino Acids and Proteins82
- Ch.19 Enzymes and Vitamins63
- Ch.20 Carbohydrates44
- Ch.21 The Generation of Biochemical Energy65
- Ch.22 Carbohydrate Metabolism45
- Ch.23 Lipids42
- Ch.24 Lipid Metabolism33
- Ch.25 Protein and Amino Acid Metabolism24
- Ch.26 Nucleic Acids and Protein Synthesis45
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook
Chapter 21, Problem 32b
The following reactions occur during the catabolism of glucose. Which are exergonic? Which is endergonic? Which proceeds farthest toward products at equilibrium?
b. Phosphoenol pyruvate + H2O → Pyruvate + Phosphate(Pi)
∆G = –14.8 kcal/mol (–61.9 kJ/mol)
Verified step by step guidance1
Step 1: Understand the terms 'exergonic' and 'endergonic'. Exergonic reactions release energy and have a negative ΔG value, while endergonic reactions require energy input and have a positive ΔG value. In this case, the ΔG value is given as -14.8 kcal/mol (-61.9 kJ/mol), which is negative, indicating that the reaction is exergonic.
Step 2: Recall the relationship between ΔG and the direction of a reaction at equilibrium. A highly negative ΔG value suggests that the reaction proceeds far toward the products at equilibrium because it is thermodynamically favorable.
Step 3: Analyze the reaction provided: Phosphoenol pyruvate + H2O → Pyruvate + Phosphate (Pi). The breakdown of phosphoenol pyruvate (PEP) into pyruvate and phosphate is a key step in glycolysis and is known to be highly exergonic, as indicated by the large negative ΔG value.
Step 4: Conclude that this reaction is exergonic due to the negative ΔG value. Additionally, because the ΔG value is significantly negative, the reaction proceeds far toward the products at equilibrium, favoring the formation of pyruvate and phosphate.
Step 5: Summarize the findings: The reaction is exergonic, and it proceeds far toward the products at equilibrium due to the highly negative ΔG value. No energy input is required for this reaction to occur.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Exergonic Reactions
Exergonic reactions are chemical processes that release energy, typically characterized by a negative change in Gibbs free energy (∆G). In the context of glucose catabolism, these reactions are spontaneous and proceed in the direction of product formation, contributing to the overall energy yield of cellular respiration.
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Endergonic Reactions
Endergonic reactions require an input of energy to proceed, resulting in a positive change in Gibbs free energy (∆G). These reactions are non-spontaneous and often involve the synthesis of complex molecules from simpler ones, which is essential for cellular functions but must be coupled with exergonic processes to drive them forward.
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Equilibrium in Chemical Reactions
Equilibrium in chemical reactions refers to the state where the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. The position of equilibrium can be influenced by factors such as temperature and concentration, and reactions that proceed farthest toward products at equilibrium typically have a larger negative ∆G, indicating a strong tendency to form products.
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Related Practice
Textbook Question
What is the difference between catabolism and anabolism?
Textbook Question
What is the difference between digestion and metabolism?
Textbook Question
Arrange the following events in the order in which they occur in a catabolic process: electron transport, digestion, oxidative phosphorylation, citric acid cycle.
Textbook Question
The following reactions occur during the catabolism of acetyl-CoA. Which are exergonic? Which is endergonic? Which reaction produces a phosphate that later yields energy by giving up a phosphate group?
c. L-Malate + NAD+ → Oxaloacetate + NADH + H+
∆G = +17 kcal/mol (+129.3 kJ/mol)
Textbook Question
Why is ∆G a useful quantity for predicting the favorability of biochemical reactions?